Previously Unknown Large Impact Basins on the Moon Revealed by Lunar Topographic Data

The discovery of a very large population of impact basins on Mars not visible in image data but revealed by MOLA topographic data raises the obvious question of whether there are previously unrecognized impact basins on the Moon. Mars has many more ways to hide impact basins than does the Moon, but the presence of significant numbers of “Quasi-Circular Depressions” (QCDs) in even the highlands of Mars does suggest that lunar topographic data should be searched for similar features that were not previously recognized by classical photogeologic mapping. MOLA-quality lunar topography will not be available until the Lunar Orbiter Laser Altimeter (LOLA) is launched on the Lunar Reconnaissance Orbiter (LRO), but the Unified Lunar Control Net 2005 (ULCN), based on Clementine stereo imagery and laser altimetry, is good enough to reveal the presence of large impact basins on the Moon. A preliminary search revealed 92 QCDs larger than 300 km diameter, compared with the 45 listed by Wilhelms based on photogeological mapping. While many of his large basins do have good topographic signatures, some have no expression in the ULCN topography at all, and his list shows a deficiency in the 300-500 km diameter range compared to the basins revealed by the ULCN data. A study of ULCN QCDs inside the large South Pole Aitken basin suggests the total (visible + previously unrecognzied) cumulative population may be 1.8 times greater at 100 km diameter than suggested by imagery alone.